Haemophilus influenzae is exclusively adapted to infect or colonize humans. Strains can be encapsulated or non-encapsulated (non-typeable). Non-typeable Haemophilus influenzae (NTHi) is a frequent colonizer of the nasopharynx and is an opportunistic pathogen. When the airway is compromised, NTHi can cause local infections such as otitis media in young children (24 million physician visits per year in the U.S. (Teele et al., (1983) JAMA 249, 1026-1029)) and chronic bronchitis and pneumonia in patients with chronic obstructive pulmonary disease. A major component of the outer membrane of H. influenzae, the lipooligosaccharides, plays an important role in microbial virulence and pathogenicity. N-Acetylneuraminic acid can be incorporated into the lipooligosaccharides as a terminal non-reducing sugar. Although much of the pathway of sialic acid incorporation into lipooligosaccharides is understood, the transporter responsible for N-acetylneuraminic acid uptake in H. influenzae has yet to be identified and characterized.